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The two-step percolation behavior in aggregating systems was studied both experimentally and by means of Monte Carlo (MC) simulations. In experimental studies, the electrical conductivity, σ, of colloidal suspension of multiwalled carbon nanotubes (CNTs) in decane was measured. The suspension was submitted to mechanical de-liquoring in a planar filtration-compression conductometric cell. During de-liquoring, the distance between the measuring electrodes continuously decreased and the CNT volume fraction ϕ continuously increased (from 10 −3 up to ≈ 0.3% v/v). The two percolation thresholds at ϕ 1 10 −3 and ϕ 2 ≈ 10 −2 can reflect the interpenetration of loose CNT aggregates and percolation across the compact conducting aggregates, respectively. The MC computational model accounted for the core-shell structure of conducting particles or their aggregates, the tendency of a particle for aggregation, the formation of solvation shells, and the elongated geometry of the conductometric cell. The MC studies revealed two smoothed percolation transitions in σ(ϕ) dependencies that correspond to the percolation through the shells and cores, respectively. The data demonstrated a noticeable impact of particle aggregation on anisotropy in electrical conductivity σ(ϕ) measured along different directions in the conductometric cell.

The Monte Carlo simulation is applied to study the impact of the aggregation on the percolation anisotropy on a square lattice in the elongated 𝐿𝑥 ×𝐿𝑦 geometry. An interactive cluster-growth model, in which the probability of occupying a site on a lattice 𝑓𝑧 is dependent on the number of occupied neighboring sites 𝑧 is used. The value of 𝑓𝑧 is 1/𝑟 at 𝑧 = 0 and is equal to 1 in other cases. The degree of the aggregation parameter 𝑟 ≥ 1 controls the morphology of aggregates. The transition from 𝑟 = 1 to 𝑟 → ∞ corresponds to the transition from the ordinary random percolation to the percolation of compact Eden clusters. The effects of the lattice aspect ratio 𝑎 = 𝐿𝑥/𝐿𝑦 (𝐿𝑥 > 𝐿𝑦) on the finite-size scaling and the electrical conductivity are studied. The data evidence that the percolation threshold 𝑝𝑐 goes through the minimum, and the finite-size effects are enhanced with increase in 𝑟. The dependence of the electrical conductivity on the measuring direction (𝑥 or 𝑦) at different values of 𝑟 and 𝑎 is discussed.

The effect of acid treatment on the structure and properties of suspensions of multiwalled carbon nanotubes (MWCNTs) in glycerol has been investigated. The concentrations of MWCNTs were within 0-2 % by weight. Suspensions were treated during 5-60 min at T = 343 K by a mixture of concentrated nitric and sulphuric acids with the volume ratio of 1:3. The degree of acid treatment influence on the structure of suspension was analyzed using methods of thermal analysis and infrared spectroscopy. Oxidation of MWCNTs could affect significantly their thermal stability and degree of destruction. The changes in the structure of MWCNT clusters in glycerol, electrical conductivity and percolation behaviour of the systems are discussed. The acid treatment is shown to cause significant decrease in conductivity of suspension and enhancement of its temperature dependence. Reduction of the length of MWCNTs after acid treatment is reported.